PPT/Module 13-14

• Virology is the scientific discipline concerned with the study of the biology of viruses and viral diseases, including the distribution, biochemistry, physiology, and clinical aspects of viruses.
• Viruses and bacteria are both types of microorganisms, but they differ significantly in terms of structure, replication, and the way they cause diseases.
• Viruses are much smaller than bacteria and are not considered living organisms.
• Bacteria are single-celled organisms with a more complex structure and are living organisms with the ability to carry out independent metabolic processes and reproduce on their own.
• Viruses cannot replicate on their own and need to infect a host cell and hijack its cellular machinery to replicate and produce more viruses.
• Bacteria can replicate independently through a process called binary fission, where a single bacterial cell divides into two identical daughter cells.
• Viral infections are typically treated with antiviral medications that target specific stages of the viral life cycle.
• Bacterial infections are commonly treated with antibiotics, which are substances that can kill or inhibit the growth of bacteria.
• Viruses are responsible for a wide range of diseases, including the common cold, influenza, HIV/AIDS, and COVID-19.
• Bacteria can cause various infections, such as strep throat, urinary tract infections, pneumonia, and bacterial meningitis.
• Viruses have no cell nucleus, do not have an organized cell structure, do not respire, do not metabolize and do not grow but they do reproduce.
• Viruses are considered both as living and nonliving things, as they are inactive outside the host cell, and are active when present inside host cell.
• Viruses contain a viral genome of ribonucleic acid (RNA) or deoxyribonucleic acid (DNA) and a protein coat — the capsid.
• Pseudovirions are virus-like particles that lack viral genomic material but can incorporate and present foreign genetic material, such as DNA or RNA, for delivery into host cells.
• Prions are unique infectious agents that consist solely of misfolded proteins, without any associated nucleic acid (DNA or RNA).
• The misfolding process in prions leads to the accumulation of aberrant proteins in the brain, causing neurodegeneration.
• Pseudovirions are often engineered for therapeutic purposes, such as gene therapy and vaccine development.
• Viroids are the smallest infectious agents known, consisting of short, single-stranded circular RNA molecules without a protein coat.
• Prions have the ability to induce normal proteins to misfold into the abnormal, infectious conformation.
• Defective viruses can interfere with the replication of the helper virus and may modulate the course of infection.
• Defective viruses are viral particles that are incomplete and require the presence of a helper virus to complete their replication cycle.
• Defective viruses often result from mutations or deletions in their genome.
• Viroids lack the protein coat (capsid) that is typical of viruses and replicate autonomously using host cell enzymes.
• The genome and its protein coat together are referred to as the nucleocapsid.
• The entire virus particle is called the virion.
• Some viruses also have a phospholipid labile envelope surrounding the virion.
• The primary distinction between DNA viruses and RNA viruses lies in the type of genetic material they possess.
• DNA viruses carry their genetic information in the form of double-stranded DNA, whereas RNA viruses carry single-stranded or double-stranded RNA.
• Ganciclovir is used to treat infections caused by cytomegalovirus (CMV), especially in immunocompromised patients (e.g., after an organ transplant).
• Famciclovir is used to treat herpes infections, including genital herpes and shingles, similar to acyclovir and valacyclovir.
• Oseltamivir is used to treat and prevent influenza (flu) caused by influenza A and B viruses.
• Interferons are proteins produced by host cells in response to viral infections and other stimuli, playing a crucial role in the innate immune response, acting as signaling molecules to induce an antiviral state in neighboring cells.
• Killed- virus vaccines generally induce a weaker immune response compared to and may require boosters to maintain immunity.
• Attenuated live-virus vaccines generally induce a robust and long-lasting immune response, often providing lifelong immunity with a single dose or a few doses.
• Entecavir is used to treat chrombinationic hepatitis B virus (HBV) infection.
• The primary antiviral actions of interferons include inhibition of viral replication, enhancement of major histocompatibility complex (MHC) expression, and activation of natural killer (NK) cells.
• Killed-virus vaccines and attenuated live-virus vaccines are two main types of vaccines used to prevent viral infections, differing in their properties, methods of production, and effects on the immune system.
• Ribavirin is used in combination with other medications to treat hepatitis C virus (HCV) infections.
• While generally safe, attenuated live-virus vaccines may pose a risk for individuals with weakened immune systems, as the attenuated virus can cause a mild form of the disease in rare cases.
• Sofosbuvir is another medication used to treat hepatitis C virus (HCV) infections, often in combination with other antiviral drugs.